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    Subject[PATCH 4.2 105/134] fs: Dont dump core if the corefile would become world-readable.
    Date
    4.2-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jann Horn <jann@thejh.net>

    commit 40f705a736eac10e7dca7ab5dd5ed675a6df031d upstream.

    On a filesystem like vfat, all files are created with the same owner
    and mode independent of who created the file. When a vfat filesystem
    is mounted with root as owner of all files and read access for everyone,
    root's processes left world-readable coredumps on it (but other
    users' processes only left empty corefiles when given write access
    because of the uid mismatch).

    Given that the old behavior was inconsistent and insecure, I don't see
    a problem with changing it. Now, all processes refuse to dump core unless
    the resulting corefile will only be readable by their owner.

    Signed-off-by: Jann Horn <jann@thejh.net>
    Acked-by: Kees Cook <keescook@chromium.org>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/coredump.c | 8 ++++++--
    1 file changed, 6 insertions(+), 2 deletions(-)

    --- a/fs/coredump.c
    +++ b/fs/coredump.c
    @@ -685,11 +685,15 @@ void do_coredump(const siginfo_t *siginf
    if (!S_ISREG(inode->i_mode))
    goto close_fail;
    /*
    - * Dont allow local users get cute and trick others to coredump
    - * into their pre-created files.
    + * Don't dump core if the filesystem changed owner or mode
    + * of the file during file creation. This is an issue when
    + * a process dumps core while its cwd is e.g. on a vfat
    + * filesystem.
    */
    if (!uid_eq(inode->i_uid, current_fsuid()))
    goto close_fail;
    + if ((inode->i_mode & 0677) != 0600)
    + goto close_fail;
    if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
    goto close_fail;
    if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file))



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